Apparatus for coupling and uncoupling propellers



Oct. 16, 1951 o. w. EHLERS 2,571,848

APPARATUS FOR COUPLING AND UNCOUPLING PROPELLERS Filed June 1.4, 1946 5 Sheets-Sheet l INVENTOR.

$31M Eh;

o. w. EHLERS 2,571,848

/APPARATUS FOR COUPLING AND UNCOUPLING PROPELLERS' Oct. 15, 1951 5 Sheets-Sheet 2 Filed June 14, 1946 5 F R mM N R M 0 m m A M W O l/ T O W 3% 0. w. EHLERS Oct. 16, 1951 APPARATUS FOR COUPLING AND UNCOUPLING PROPELLERS 5 Sheets-Sheet 3 Filed June 14, 1946 Kw w mm .n W W 0mm v Oct. 16, 1951 o. w. EHLERS APPARATUS FOR COUPLING AND UNCOUPLING PROPELLERS 5 Sheets-Sheet 4 Filed June 14, 1946 R E T S O O B INVENTOR. Offo l f/f/h'am Eh/ers Kim 31 T RNEY Oct. 16, 1951 Q w EHLERS- 2,571,848

APPARATUS FOR COUPLING AND UNCOUPLING PROPELLERS I Filed June 14, 1946 5 Sheets-Sheet 5 BOOS TEP- INVENTOR. 0H0 Will/am Eh/ers for Patented Oct. 16, 1951 APPARATUS FOR COUPLING AND UN COUPLING PROPELLERS Otto William Ehlers, Hermosa Beach, Calif., assignor to Consolidated Vultee Aircraft Corporation, San Diego, Calif., a corporation of Delaware Application June 14, 1946, Serial No. 676,783

12 Claims.

This invention relates to improvements in airscrew propulsion devices and more particularly to the coupling system between the engine and the airscrew it drives.

The invention to be described herein is particularly adapted for use in gas-turbine enginepropeller combinations for aircraft. -With this invention it will be feasible to utilize both the propeller and the gas-turbine engine and to use each to full advantage. Phe greater speed obtainable by the use of jet propulsion over the speed provided by propeller propulsion devices is obviously desirable. However the use of a propeller has many advantages. For instance, the take-oif distance required by an airplane utilizing a propeller is very much less than that of an airplane employing jet-propulsion.

This becomes an important criterion in the case of heavy military craft and large transports, which, if they had to rely on jet propulsion alone, would require flying fields of much larger dimensions than are currently readily available. Furthermore, the propeller can. cope with emergency conditions more readily than the jet propulsion unit. For instance, if the pilot should overshoot the field in landing and require, instantly, the maximum thrust obtainable from the engine. to sharply lift the airplane, the propeller can provide the needed thrust whereas the jet propulsion engine would be inadequate.

Likewise at low speeds, as when the airplane is coming in for a landing, the jet propulsion engine is very inefficient as compared with a propeller-engine combination.

With the present invention it is possible to employ both the propeller and the jet propulsion engine and obtain the best. flying characteristics of each. The jet propulsion engine will perform a dual role, it will drive a propeller when it is advantageous to do so, as in take-off, climb and landing, and will be uncoupled from the propeller cruising. The coupling system disclosed herein adapts the propeller to be readily and tinci-ently coupled and. uncoupled from the jet propulsionunit while the airplane is in flight.

It is therefore an. object of the present invention to provide inv an engine-propeller propulsion unit a novel system for effectingthe coupling and uncoupling of. the propeller to and. from the engine.

Another object of the invention is to provide in an engine-propeller combination improved means to eifect synchronism of the speeds of the propeller shaft and the engine drive shaft.

Another object of the. invention is to provide in a turbine engine-propeller, combination an improved coupling system whereby the turbine engine may be used in combination with the propeller, or used alone, to propel an airplane.

Another object of the invention is to provide in a propeller-engine combination for airplanes, improved means for actuating a movable coupler element in reverse direction to effect coupling or uncoupling of the propeller from the engine while the airplane is in flight.

Another object of the invention is to provide in a propeller-engine combination improved mechanism for effecting the synchronizing of the movement of the propeller shaft with that of the movement of the engine shaft and for moving a coupler element when synchronization is obtained to effect coupling or uncoupling of the propeller from the engine.

Another object of the invention is to provide in a propeller-engine combination an improved form of coupling system embodying a clutch device.

Another object of theinvention is to provide in a propeller-gas turbine engine combination wherein the propeller drive shaft and the gas turbine engine drive shaft are provided with splines, an improved coupling system which utilizes mechanism for synchronizing the speeds of the two shafts and for positively aligning the splines of the gas engine drive shaft with the splines of the propeller drive shaft.

Another object of this invention is to provide a coupling system of the type referred to which is characterized by simplicity of design and efliciency of operation.

Other objects and features of this invention will be readily apparent to those skilled in the art from the following specification and appended drawings illustrating certain preferred embodiments in which:

Figure l is a schematic showing of one form of the invention, but with certain of the electrical devices employed by the invention and their electrical leads omitted for clarity of illustration,

Figure 2 is a schematic. showing of another embodiment of the invention, which is similar to that of Figure l, but differing thereover in the use of clutch mechanism,

Figure 3 is an illustration of the coupler elements of the embodiment of Figure 1 and in the position. assumed by such elements when the propeller is uncoupled. from the gas turbine engine,

Figure 4 is a sectional view taken alon the line IV-IV of Figure 3,

Figure 5 is a perspective view of the coupler elements of the embodiment of Figure 2,

Figure 6 is a longitudinal sectional view of the coupler elements of Figure 5 and showing the elements in uncoupled position,

Figure 7 is similar to Figure 6 but with the coupler elements shown in coupled position wherein the propeller drive 1 shaft is coupled to the gas turbine engine drive shaft,

Figure 8 is a vertical sectional view taken along the line VIHVIII of Figure '7,

Figure 9 is a detail view showinga solenoid employed by the present invention,

Figure 10 is a diagrammatic illustration of the first embodiment of the invention emphasizing the electrical circuit employed and omitting certain structure for clarity, and

Figure 11 is a diagrammatic illustration of the second embodiment of the invention differing over Figure 1G in the inclusion of a clutch means and the manner of control thereof.

Referring to Figure l, the system therein disclosed comprises a propeller l carried by a hub H which is mounted on a shaft 2. Disposed forwardly of the hub II is a spinner l3 which houses a propeller governor l4 and pitch control gearing l5. The details of the governor l4 and the gearing l are not shown because their exact construction forms no part of the present invention. They may be of any conventional design. The purpose of this governor mechanism within the spinner I3 is to provide a means for controlling the speed of the propeller it by regulating the pitch thereof. Changing the pitch of propeller ID will affect the speed of an engine to which it is coupled in that the propeller can be made to absorb more or less power, thereby decreasing or increasing the engine speed to bring it to a predetermined value set on the governor. Located on the propeller shaft I2 rearwardly of hub is a ring gear |6 which meshes with a ring gear 31 which effects the operation of an alternator |8. The alternator |8 is of a conventional design and is a three-phase alternating current generator which generates an alternating current voltage, the frequency of which will be directly proportional to the speed of the propeller shaft l2.

Aligned with the propeller drive shaft I2 is an engine drive shaft 2| which also carries a ring gear 22. The gear 22 meshes with a ring gear 23 which operates an alternator 24. The alternator 24 is similar to alternator l8 and also generates an alternating current voltage, the frequency of which will be directly proportional to the speed of the engine drive shaft 2|. The engine drive shaft 2| is of hollow construction and houses areversible constant speed electric motor 25 the purpose of which will be hereinafter described.

The propeller governor M, the alternators l8 and 24, and the motor 25 are all electrically connected by means of suitable conductors to a synchronizing control unit 21, the operation and details of which will be later described.

A gas turbine engine 3| provides the motive power for turning the engine drive shaft 2| and thereby the propeller H3. The gas turbine engine 3| is of conventional design and comprises the usual compressor 32, turbine 3-3, with a shaft 34 interconnecting the compressor 32 and the turbine 33, a fuel injector 35, combustion chambers 36, a nozzle 31 and conventional reduction gearing 38 interconnecting the engine drive shaft 2| to the compressor whereby the engine drive shaft 2| is actuated. The exact construction of the gas turbine engine 3| forms no part of the present invention.

Figure 3 illustrates mechanism whereby coupling is obtained between the engine drive shaft 2| and the propeller drive shaft 12. As shown these drive shafts are respectively provided with bores 4| and 42 therethrough, the shafts being in alignment and the bores 4| and 42 being of equal diameter. The constant speed electric motor 25 is mounted Within the bore 42 of engine drive shaft 2|. It is rigidly held in place by brackets 43 which in turn are secured to the inner surface of the shaft 2|, as by welding or in any other well known manner.

Formed in the pass-age 4| of drive shaft |2 are a plurality of annularly spaced longitudinally extending splines 44. Similarly in passage 42 of engine drive shaft 2| annularly spaced longitudinally extending splines 45 are provided and adapted to align with splines 44. The ends 45 of the splines 44 in the propeller drive shaft l2 are substantially pointed as shown for a purpose to be described.

Disposed in passage 4| of engine drive shaft 2| and rectilinearly movable therein is a substantially cylindrical coupling member 41. As seen in Figures 3 and 4 the outer periphery of the coupling member 41 is provided with a plurality of longitudinally extending grooves 48 to effect a plurality of annularly spaced splines 5|. The grooves 48 are adapted to receive the splines 45 of the engine drive shaft 2|. The ends of splines 5! disposed adjacent ends 46 of splines 44 are also pointed. The coupling member 41 has an internally threaded bore 52 extending therethrough. A worm drive element 53 is adapted to coact with the internally threaded bore 52. The worm drive element 53 is enlarged at one end to provide a substantially cylindrical portion 54 having a recess 55 therein with the interior surface of the recess being splined. From the motor 25 there extends a shaft 51 having an enlarged portion 58 which fits into the recess 55. The outer surface of the portion 58 is grooved to receive the splines in recess 55 and thereby provide an interconnection between the worm drive element 53 and motor 25 whereby the former may be rotated upon operation of the motor 25. The shaft portion 58 and the worm drive portion 54 are maintained in interconnection by a drive fit, although they could be maintained by the use of'any other well-known fastening expedients. such as by set-screws, tapered pins or brazing. Rotation of the worm drive 53 will cause the coupler 41 to move along the trackways provided by splines 45 in bore 42, into the propeller drive shaft passage 4| wherein the splines 5| carried by coupler 41 mesh with the splines 44 in passage 4| and thereby couple the engine drive shaft 2| to the propeller drive shaft |2 for common movement. Reverse rotation of the worm drive 53 will move the coupler 47 in the reverse direction to effect uncoupling of the shafts |2 and 2|. Having the ends 46 of splines 44 in passage 4| and the ends of splines 5| on coupler 41 pointed obviously permits the splines 5| to more readily enter passage 4| and mesh with splines 44. Shoulders Bl are provided on certain of the splines 45 of the engine drive shaft 2| to limit the rearward longitudinal movement of coupler 41. Similar shoulders (not shown) are provided on certain of splines 44 in passage 4| to limit the longitudinal movement therein of coupler 41.

The equipment for controlling the time of starting and stopping of motor 25 is shown in Figure 10 to be hereinafter described.

Figuresiz and 5 through 9 illustrate aseeond form of coupling system utilized by the. present invention. This coupling system differs from the coupling system above described in the provision of a clutch means 64. As does the coupling system first described, this system, as shown in Figure 2, comprises a propeller governor unit [:4 with its associated gearing l5 for controlling propeller is; a hollow propeller drive shaft I2 having annularly spaced longitudinally extending splines 44; a hollow engine drive shaft 2:| aligned with the shaft |2; alternators l8 and 24 associated with shafts l2 and 2|; annularly spaced longitudinally extending splines 45 in engine drive shaft 2|; an exteriorly splined coupling member 41 slidably movable in engine drive shaft 2| on the splines 45'; a worm drive 53 for actuating the exteriorly splined coupler 41 into an out of propeller drive shaft l2, and a constant speed electric motor 25 connected to the worm drive 53 for rotation of the worm drive 53 in opposite directions.

The clutch means 64 includes ahousin 55 having a generally cup-shaped portion 65 and a cylindrical portion 61 of smaller diameter extending from the base thereof and having an interiorly splined bore 68 extendingtherethrough whereby the cylindrical portion 61 is adapted to be fitted upon the exteriorly splined end H of the propeller drive shaft l2. The exteriorly splined end H of propeller shaft l2 cooperates with the interiorly splined bore 68 to key the cylindrical portion 61' of housing 65 in position. The housing 65 is rigidly secured to the propeller shaft |2 as by'bolts T2. The cup-shaped portion 56 extends outwardly from the end ll of the propeller drive shaft l2 and embraces a substantial portion of the forward end 14 of the engine drive shaft 2|.

As shown in the drawings this clutch 64 comprises twelve solenoids 16 arranged in two sets of. six, in side by side relationship, and annularly disposed and equally spaced about the engine drive shaft 2|. It is to be understood that the invention is not limited to the number of solenoids shown; the number of solenoids used being dependent upon a variety of factors: The size of the propellers to be coupled and uncoupled, the weights of the mechanism employed, etc.

The solenoids. it are secured to the inner surface of the cup-shaped portion 6% by bolts 11 which pass through ears provided by enclosing casings 78' of the solenoids 16.

A bushing BI is fitted upon the end M of the engine drive shaft 2| and is secured thereto as by rivets ("not shown). The bushing 81 carries a bearing sleeve 82 which may be of brass or similar material. The bearing sleeve 82 is held in place by rivets, (not shown) or in any other well known manner. The bearing sleeve 82' is provided with a series of spaced indentations 83 about its periphery as shown in Figure 8, there being as many indentations 83 as there are annularly arranged pairs of solenoids E6, in this instance siX. The indentations 83 extend longitudinally and each are of sufficient length to receive a brake shoe 84. There are six brake shoes 84, one for each of. the indentations 83, and each brake shoe B4 is carried by a pair of solenoids 18. The brake shoes 84' are each of a generally channel shape comprising an' arcuate bearing portion 85 of a conformation similar to thatv of indentations 83 for ready seating therein; from the arcuate portion 85. extend spaced leg members 86 and 81. Depending" from the inner: surface of the arcuate portion 85; and; between. the parallel leg members 85, andBS are a pair of longitudinally spaced bosses 88'. The bosses 8.8 are provided with internally threaded recesses adapted to receive the externally threaded end '93 of a movable core member 94 of" a solenoid 16. The solenoids 76 may be of the general construction shown in Figure 9. As illustrated, each solenoid 76 comprises a casing 18.. housing the core element 94, one end 93 of which is threaded, as statedabove, and the other end of which carries an extension 95. having'a contact 9'0 secured thereto. Asleeve member 9.! is: disposed-about the core member 94. A washer disposed in the sleeve 9;! accepts the extension 85 and limits the inward travel of the coreelement 94- into the casing 18. Coil means 98 are provided within casing 18 and about the sleeve 9"! for actuation of the core element 94 upon energization thereof. Located adjacent the inner end of core element Q4 is a spring biased contact |0| adapted to cooperate with the contact 96; movementof' the-core 94 effects engagement and disengagement of contacts 96 and lli l to make: and break an electrical circuit for a purpose tobe hereinafter explained. A stop [52 limits the travel of the spring-biased contact |-El'| in the direction of its engagement with contact 96 so that the latter contact 96 can definitely disengage therefrom when so desired. As shown the upper end of the solenoid casing 18 has a recess I63 provided to accept the boss carried by brake shoe 84.

Disposed within the clutch housing and equally spaced about the inner periphery thereof, as best shown in Figure 8, are a plurality of guide members I04, with one guide member located between adjacent aligned pairs of solenoids E6. Each guide member I94 comprises a generally arcuate portion Hi5 which is adapted to be welded or otherwise secured to the inner surface of the clutch housing 65, and a pair of leg members |fl6and I91 which are inclined toward one another. The legs I96 and NW of each guide member H14 cooperate with the leg members IE6 and Ill! of adjacent guide members I04 to provide parallel guide surfaces between which move the spaced leg members 8% and 81 of brake shoes 84 to thereby guide the shoes for rectilinear movement. The brake shoe leg members 86 and 81 are provided with slots which accept the shanks I I2 of guide pins i l3 carried by leg members I08 and H11.

Figure 10 illustrates diagrammatically the equipment associated with the coupler system of Figure 3 for controlling the starting and stopping of motor 25 and thereby effect the coupling and uncoupling of propeller drive shaft l2 and engine drive shaft 2|. For clarity structural details relatingto the propeller, its shaft, gearing, gas turbine-engine, coupler, worm drive, etc., are omitted, and only that portion of the engine drive shaft 2| housing the electric motor 25 is shown,

As shown, the invention employs an engine tachometer |2| and a propeller tachometer |22. The engine tachometer |2.| is used to. determine the engine. speed and the propeller tachometer I22 toindicate propeller speed. By reading these dials the. pilot of an airplane utilizing the present invention determines the moment, as will be further explained hereinafter, at which he will throw either the couple switch I23 or the uncouple. switch. I14 to effect the actuation of the coupler elements above described to couple or The electric switches I23 of indicator lamps I38 and I3I are associated with switches I23 and I24 to indicate when these switches are in operation. Leads I25 and I25 interconnect the switches I23 and I24 with stationary contacts H9 and I26 of a motor actuating relay switch I2I. Movable contacts I28 and I29 of relay switch I27 cooperate with stationary contacts H9 and I28 and are normally spring biased for engagement therewith. The motor actuating switch I21 directly controls the starting and stopping of motor 25. A coil I34 effects actuation of the movable contacts I28 and I28 of switch I21 to disengaged position. Leads I32 connect the movable contacts I28 and I29 to a double-throw limit switch I33, of conventional design, located in the circuit of motor 25. As shown one contact I35 oi the limit switch I33 is in closed position and the other contact I36 is in open position. The operation of limit switch I33 is directly dependent on the motor 25. Each time that the coupler 4! is brought to couple or uncouple position by the motor 25, the limit switch I 33 will be actuated to move the closed contact to open position and the opposite contact to closed position, stopping the motor 25 and preparing it for reverse operation, as will be further explained.

A conductor l3! connects the coil I34 of relay switch I21 to the propeller governing unit I4 which regulates the pitch of the propeller. When electrical power is flowing through propeller unit I4, the power being provided by synchronizing control unit 21, the coil I34 being connected to the propeller governor unit I4 through conductor I31 will be energized and the contacts of motor actuating switch I21 will be open.

A conventional selector switch I38 controls the operation of the propeller governor unit I4, being connected thereto by leads I4I and I42. This switch has three positions: Increase, Decrease, and Oil. With the selector switch in off position the propeller will operate as a fixed pitch propeller. 'Io adjust'the blade angles of the propeller, the selector switch contact blade is manually held at the increase or the decrease position dependent on Whether an increase or decrease in the speed of the propeller is desired. With the desired speed attained the switch arm is moved to off position and the propeller will operate at the pitch determined by the previous movement. The selector switch I38 provides a means for placing control of pitch changes in the hands of the pilot.

Leads I43 interconnects the couple switch I23 with the selector switch I38. A lead I44 connects the uncouple switch I24 to lead I42 extending from switch I 24 to propeller governor unit I4, and a lead I45 connects the selector switch I33 to a feathering switch I46.

The feathering switch I45 is of conventional design and comprises two switch arms I4! and I48 which are respectively actuable to feather and normal positions, the feather position being marked F and the normal position being marked N on the drawings. Movement of the switch arm I48 from normal position to open position removes selector switch I38 out of circuit with the propeller governor unit I4 and prevents changes in pitch of propeller I by switch I38. Actuation of the switch arm I4! to "feather position will effect operation of the governor propeller unit I4 to place the propeller I0 in feathered condition.

A selector relay operated switch I53 provides means for actuating the couple switch I23 and uncouple switch I24 as will be further explained. The selector relay switch $53 is of the usual construction and comprises a pair of stationary contact I54, a movable contact arm carrying the movable contacts I55, the movable contacts being normally held in disengaged position by a solenoid I56. Leads I57 connect the switch I53 to the solenoid coils of the couple switch I23 and uncouple switch I24.

A conventional thermal relay switch I58 is associated with the selector switch I53 to control the'operation thereof. The thermal relay switch I58 comprises a stationary contact, a movable contact carried by a bimetallic element I6I which normally engages the stationary contact, and a coil I62 through which current flows to effect the flexing of the thermal element I8I to disengage the contacts. While the contacts of the thermal relay switch I58 are in engagement a circuit is completed through the solenoid I56 of selector switch I53 and its contacts will be maintained in open position. The operation of the switches I58 and I53 will be hereinafter further described. A lead I83 interconnects the thermal relay switch I53 to the motor circuit 25.

A battery I59 through appropriate leads provides power to the various switches of the system. A power boost unit I60 is associated with-the battery I59. The power boost unit I68 may be of any well known construction and its function is to insure that sufiicient power will be provided when fast feathering of the propeller is required. The specific construction of the power boost unit I69 forms no part of the present invention.

The engine tachometer I2I is connected by conductors I5I to the engine alternator 24 and the propeller tachometer I22 is connected'by conductors I52 to the propeller alternator I 8. The engine alternator 24 and the propeller alternator I8 are electrically connected to the synchronizing control unit 21 by suitable conductors. The purpose of the synchronizing control unit 21 is to effect synchronization of the speed of the propeller drive shaft I 2 with that of the engine drive shaft 2I through the propeller governor unit I4 and the propeller alternator I8 and the engine alternator 24. As shown the synchronizing control unit 21 comprises a direct current reversible constant speed motor I64 which is operated from the engine alternator 24, leads I5I interconnect motor I64 with engine alternator 24. The motor I84 is mechanically interconnected with a threephase armature or stator I65 embodied in a hysteresis motor I86 and the armature I65 will rotate at the speed of motor I64. Leads I67 connect the propeller alternator I8 to the armature I65 through slip-rings I68 whereby the propeller alternator can impress a three-phase alternating current voltage on the armature. This voltage will create a magnetic field which rotates about the armature I65 whose rotation, as has been stated, is governed by motor I64. The magnetic field will rotate only as fast as the difierence between the speed of the propeller alternator I8 and that of the motor I 54 (which is also the speed of the engine alternator 24). The direction of rotation is determined by the relationship between the speed of the alternator I8 and that of the motor I64, that is, the magnetic field will rotate in either direction dependent upon whether the alternator I8 is turning faster or slower than the motor I64. If both are rotating at the same speed the magnetic field will be motionless. A magnetic drag cup or rotor III is included in the hysteresis motor I66 and is disposed about the armature I65. The magnetic dragcup III is magnetizable by the rotating magnetic field and will rotate at the same speed and in the same direction as the magnetic field. The direction and speed of the drag cup I'll will determine through a contact and relay system HQ the direction and average rate of corrective electrical impulses to be transmitted to the propeller governor unit It from the synchronizing control unit 27, the electrical power provided the governor unit It will effect control of the speed of propeller I by effecting an adjustment of the angles of the propeller blades; this-operation will be more fully described hereinafter.

The contact and relay system I12 includes a commutator II3 mechanically associated with the drag cup I'II, an interrupter relay H 3 and a propeller relay H5, both electrically interconnected with the commutator H3. The propeller relay I15 comprises a pair of solenoid coils I'IG disposed on either side of a pivotally movable I armature II? which carries a pair of movable contacts N8, the movable contacts I18 being adapted to engageand disengage with a pair of stationary contacts II9, upon pivotal movement of the armature IT! by solenoid coils I'Ifi when these coils are energized by current transmitted from commutator H3. A conductorifil connects the movable contacts II8 through contact block I80 to the coupleswitch I23 and the uncouple switch I24. Leads I82 and I83 connect the stationary contacts I19 to the propeller governor unit It through contact block I39. When'the left hand contact set I'I8 I'I9 is closed the'propeller governor unit It is adapted to operate to increase the speed of the propeller I0 by appropriate changes in the pitch thereof; when the right hand'contact set is closed the speed of the propeller is'decreased. The energization of one or the other of thesolenoid coils I16 is controlled by a contact assembly I84. The contact assembly H34 comprises a pair of spaced stationary contacts I85 electrically connected to the solenoid coils I16, and a movable contact I85 mechanically actuated between these two stationary contacts by the commutator I13. which the commutator I73 is turning determines which stationary contact I85 is engaged and therefore whichcontact set I'III I'IQ is closed. Dependent on which contact set I'm-419 is closed, the propeller governor unit It will operate to increase or decrease the'speed of propeller It. The interrupter relay I'M is-conn'ected in parallel with the'propeller relay coils I16. Its function is to break the ground return of the propeller relay I15 after the circuit through the relaycontacts II8-II9 has been momentarily established. A resistor I8! is associated with each solenoid coil I16 to maintain current in these coils for a short period of time after interrupter relay I14 opens and thereby hold the relay contacts II8I'I9 closed for a longer period of time to'permit-th'e'governor unit It to operate for a long period oftimeto effect pitch changes inthe propeller III. When there is a difierence inrspeed between the propeller alternator i 8 and the motor I64 there will be a rotation of the magnetic field-in the hysteresis motor I66 to rotate drag cup'I'II and operate commutator H3 to provide'corrective impulses of current to --;be transmitted to one or the other of thestationary The direction in contacts I of contact assembly I84. If the propeller alternator I8 is running slower than the motor I64 (and the vengine alternator '2 current will pass to the solenoid coil I'IB which closes the contact set IIB-I I9 that causes the propeller governor unit I4 to operate to effect an increase in the speed of the propeller I I). When the speed of the propeller It becomesthe same as the speed of the engine alternator 24 the commutator I13 will cease to feed current. If the propeller alternator I3 is running faster than motor I64, the system above described feeds corrective impulses of current to bring about a pitch change of the propeller It which decreases its speed, and thereby decreases the speed of its drive shaft I2.

The construction and details of the synchronizing control unit 21 above described form no part of the present invention. Any automatic device can be used which will affect the operation of w the propeller governor unit I4 to cause it to function to bring about a change in the speed of the propeller It and its drive shaft I2 to make the speed correspond to the speed of the engine shaft I2. It is understood that the unit 2? here shown and described is merely an illustration of one means of securing the desired changes in the speed of the propeller ID, and effecting synchronism between the speeds of the propeller drive shaft I2 and the engine drive shaft 2 I.

The operation of the embodiment of the invention above described will now be described. Assuming the airplane utilizing this first embodiment of the invention has reached a cruising altitude and it is desired to uncouple the propeller In from the gas turbine engine 3i and rely only on the latter for propulsion, the pilot must, before operating uncouple switch I24, first provide a condition where the propeller torque and the engine torque are substantially in balance, that is the torque produced by the propeller IiI- in windmilling is substantially the same as the torque produced by engine M in idl ing condition; at such a point neither is doing work on the other even though they are coupled together and rotating at the same speed because they are coupled together. The pilot obtains this point of substantial balance by throttling the speed of the engine 3| through mechanism (not shown) and actuating the'prcpeller governor-unit I4 through the selector switch I38 to--eifect a windmilling condition of the propeller III. A pilot knowing his airspeed and altitude can effectively and very'closely approximate this point of balance.

.After the pilot has determined that thepropellerr'andengine torques are substantially in balance the'uncoupling-switch I-24is actuated to complete the circuits to the motor actuating relay switch I27, the propeller governor unit I l. synchronizing control unit 27 and the selector switchIiS. Since the propeller shaft It and the engine drive shaft ii are operating at the same speed, no current is beingfed from control unit 21 to ,propeller governor unit I4, and therefore solenoid coil I34 of motor actuating relay switch I21 will be deenergized-and the movable. contacts I28 and I29 will-bein-engaged position. With its contacts engaged completion of the circuit to the motor actuating relay-switch IZILby uncouple switch I2 l will cause themotor-ZS to operate, rotating the worm drive 53 to withdraw thecoupli'ng memberll from propeller shaft I2 and rectilinearly move it into .engine drive shaft 2 I. As soon -as the couplingmember All has been completely withdrawn fromv propellereshaft I12 and it is uncoupled from the engine drive shaft 2I, the limit switch I33 is adapted to be operated with contact I35 moving to disengaged position breaking the motor circuit and stopping motor 25. At the same time contact I33 moves to engaged position to prepare the motor circuit for coupling operation.

At the time the circuit to the motor actuating relay switch I2? is completed by operation of uncouple switch I24 current will begin to flow through the coil of thermal relay switch I58. The thermal relay switch I58 is so calibrated that as soon as the coupling motor 25 has completed its action of withdrawing the coupling element 41 from propeller shaft I2 the bimetallic member i8I will have been sufficiently heated to flex outwardly to break the circuit to solenoid coil I55 of selector switch I53 deenergizing this coil and thereby permitting the movable contacts I55 to move under spring action into engagement with stationary contacts I54. With the engagement of these contacts, the solenoid coil of uncouple switch I24 is energized to efiect kicking out of this switch and placing it in inoperative position. The feathering switch I45 is next operated; the normal switch arm I48 is moved to open position and the feathering switch arm I41 is placed in closed position to operate the propeller governor unit I4 to effect movement of the propeller I5 to feathered position. The thermal relay switch I58 is so designed that the bimetallic element I6l does not return to unfiexed position for a predetermined period of time so that the operations above described will be fully completed before solenoid coil I55 of selector switch I53 is again energized to disengage movable contacts I55 and break the circuits through selector switch I53. At this time the entire system returns to a neutral condition and is ready for the coupling operation. The propeller I5 will be disconnected from the engine drive shaft 2i and will be feathered and the airplane can then be flown on jet reaction alone. If desired solenoid coils may be associated with the normal switch arm I48 and the feathering switch arm E41 which are energizable by selector switch I53 to automatically move these switch arms to required position.

When the airplane is to he landed the propeller shaft I2 and the engine drive shaft 2I must again be coupled. To efiect the coupling of these shafts the pilot will throttle the engine 3I until it is in an idling condition and will manually operate feathering switch arm I41 to disengaged position and thereby release the propeller II) for windmilling action. He will then operate the couple switch I23 to effect energization of the synchronizing control unit 21. Solenoid coil I34 of motor actuating relay switch I21 will be energized by power supplied by the propeller governor unit I4 to hold the contacts of switch I21 open to prevent the operation of motor 25. If there is any discrepancy between the speed of the propeller I0 and the engine drive shaft 2I there will be a difference in the speeds of the propeller alternator I8 and the engine alternator 24 associated therewith and therefore the magnetic field of the hysteresis motor I66 will rotate to effect a rotation of the drag cup I1I. Rotation of the drag cup "I will operate through commutator I13 to feed current through contact assembly I84 and a contact set I18I19 to the propeller governor unit I4 which will operate to change the pitch of the propeller I0 and thereby change its speed. Current will continue to be fed to the governor unit I4 until the speeds of the windmilling propeller and the engine drive shaft 2I are in substantial synchronism. At this point no further current will be passed to the governor power unit I4 from control unit 21 and current will cease to fiow in lead I31 to solenoid coil I34 whereby the coil will be deenergized and the movable contacts I28 and I29 of the motor actuating switch I21 will move to engaged position completing the motor circuit and causing motor 25 to operate. Motor 25 will then effect rotation of the worm drive 53 to rectilinearly move the coupling element 41 into passage 4I of propeller drive shaft I2. As described hereinbefore the ends of the exterior splines carried by the coupling element 41 and the ends 46 of splines 44 disposed in passage 4| are pointed to permit the two sets of splines to more easily and readily mesh. As soon as coupling of the shafts I2 and 2| has been effected the limit switch I33 will be actuated with contact arm I38 thereof moving to disengaged position to break the motor circuit and stop the motor 25. Arm I35 of the limit switch I 33 will be moved to engaged position to prepare the motor circuit for the reverse, or uncoupling, operation of the coupler element 41.

The thermal relay switch I58 will operate, as in the uncoupling operation, to effect the deenergization of solenoid coil I of switch I53 to permit the movable contacts I55 thereof to move to engaged position and thereby effect energization of the solenoid coil of couple switch I23 to move the switch arm thereof to disengaged position cutting off the flow of power to the synchronizing control unit 21. Switch arm I48 of feathering switch is then actuated to norma position to render the pitch control switch I38 manually operable and permit manual con trol of the propeller governor unit I4.

The electrical system employed with the second embodiment of the invention is diagrammatically illustrated in Figure '11. This system differs from that of the first embodiment shown in Figure 10 primarily in the provision of means for controlling the operation of the clutch 64 utilized by the second embodiment.

As shown, this second circuit also comprises an engine tachometer I2I and a propeller tachometer I22; a couple switch I23a and uncouple switch I24c electrically connected to a motor actuating relay switch I21 which latter governs the operation of the motor 25 to effect the movement of the coupler element 41 into and out of the propeller shaft I2; the couple switch I23a and uncouple switch I24a differ from the couple switch I23 and uncouple switch I24 of the first embodiment in the provision of an additional contact set; a propeller governor unit I4 for controlling the pitch of the propeller; a pitch control switch I38 electrically associated with the propeller governor unit l4 whereby the pilot can effect operation of the governor unit to change the pitch of the propeller; a feathering switch I48 to provide for normal and feathering operations of the propeller; a selector relay switch I53a. adapted to kick out the "couple and uncouple switches I23 and I24 to break the circuits therethrough; selector switch I53a difiers from selector switch I53 of the first embodiment in providing an additional contact set I54I55: a thermal relay switch I58 for controlling the operation of the selector relay switch I53; a battery I68 for supplying power to the various switches of the system; and a synchronizing unit ama e 21 associated with the propeller governor unit I4 and having a propeller alternator I8 and engine alternator 24 connected thereto whereby the synchronizing unit 21 can act upon the propeller governor unit I4 to automatically bring about a change in the pitch of the propeller and change the speed of the propeller drive shaft I2 to effect a synchronization of the speed of the propeller shaft 52 and the engine drive shaft 2I.

In addition to the above elements which are common to the electrical circuits of both embodiments of the present invention, Figure 11 illustrates diagrammatically the clutch housing 65 enclosing a solenoid I6. For ease of description but one of the twelve solenoids I6 and its cooperating contact set 96IOI is shown associated with the other elements of the electrical circuit. It is understood that the other solenoids I6 will be similarly connected into the circuit and will operate in like manner as the solenoid I6 is to be described.

The energy for effecting energization of the solenoid coil 58 of solenoid I6 is taken from a power bus I through a conductor 202. A second conductor 203 leads from solenoid coil 98 to a clutch controlling switch 204. The switch 204 includes a first contact set comprised of a stationary contact 205 and a movable contact 205 normally spring-biased into engagement with the stationary contact 205, and a second contactset comprised of a stationary contact 201 and a movable contact 208 also normally springbiased into engagement with its cooperating stationary contact 201. A solenoid coil 2Il is adapted to move the movable contact 206 to disengaged position while solenoid coil 2I2 will effect movement of movable contact 208 for disengagement. The solenoid coil 2II is connected by a lead 2 I3 to propeller governor unit I4. The solenoid coil 2I2 is connected by a first conductor 2M to the selector relay switch I530, and by a second conductor 2I5 to the couple switch E2311 and to the uncoupl'e switch I 24a.

Coil I34 of the motor actuating switch I21 in the circuit of Figure 11 instead of being electrically tied directly to the propeller governor unit I 4 is connected by lead 2I6 to the contact 96 carried by the movable core member 94 of solenoid 15. The spring-biased movable contact IOI associated with contact 96 is connected by lead 2i! to battery I60. 7

The uncoupling and coupling operations of the first embodiment of the invention has been described. Th operation of the second embodiment of the invention illustrated in Figures 2, 5 through 9 and, 11 to effect coupling and uncoupling of the propeller shaft I2 and the engine drive shaft follows.

As in the operation of the first embodiment when the plane has reached an altitude at which it is desired to rely only on the gas turbine engine 2 for propulsion the pilot must first effect a substantial balance between the torques produced by the propeller shaft I2 and the engine drive shaft 2 I. This is done by placing engine 3! inan idling condition and changing the pitch of propeller II) through the selector switch I38 and propeller governor unit It. At. such time as the pilot determines that the torques are in substantial balance the uncouple switch I24a is operated to connect the synchronizing control unit 27 and the motor actuating switch I27 in circuit. Since the propeller drive shaft I2 and engine drive shaft 2I, being coupled, are turning at the same speed there Will be no curi4 rent flowing through the propeller relay switch I15 of synchronizing control unit 2''! and therefore there will be no current being provided to the propeller governor unit I4 from the synchro-- nizing control unit 2?. Therefore no current willpass from the propeller governor unit It to the solenoid coil 2-H of the clutch controlling switch: 204 and it will be deenergized whereupon contacts 205 and 206 will engage closing the circuit through the solenoid coil 98 of clutch solenoid. I6 and permitting power to be supplied thereto from the power bus 2M to move core member 94' to its outer position and hold it in this position. All of the clutch solenoids it will operate in like manner. With the clutch solenoids I6 energized the brake shoes 84 connected to the core members 94 will be moved to seated position in the indentations 83 in bearing sleeve 82 which is carried upon the exterior of the engine drive shaft 2 l With the brake shoes 84 in their seated position and the core members 94 which actuate the brake shoes 84 in their outermost position each of the contacts 96 carried by the core members 94 will be disengaged from its associated contact IIBI and the circuit to solenoid coil I34 of the motor actuating switch I21 will be broken so that the coil I34 will be deenergized and the movable contacts I28 and I29 of switch I2! will be placed by spring action in circuit making po-'- sition and power can be fed from the battery I60 through uncouple switch I'24a to the windings of motor 25. Motor 25 will operate to effect rotation of the worm drive 57 to rectilinearly move coupler element 41 and withdraw it from passage 4| of propeller drive shaft I2. As soon as the coupler member 41 is completely withdrawn from the propeller drive shaft I-2 the limit switch I 33 is adapted to be operated to break the motor circuit and stop the motor 25. Contact arm I35 will move to open position and contact arm I36 will move to closed position preparing the motor 25 for its next operation in the reverse direction for'reverse movement of coupler member c1.

Simultaneously with the stopping of the motor 25 the thermal relay switch E58 will operate for its bimetallic member E53 will have been heated a sufiicient amount to flex and break the circuit through solenoid coil $56 of selector switch I53a deenergizing the coil and permitting the movable contacts i55 to move to circuit making position. Movement of movable contacts I55 to contacts engaged position will effect energization of solenoid coil 2H2 of clutch controlling switch 2% to disengage movable contact 208 from its cooperating stationary contact 2t! breaking the circuit to solenoid coils 98 of clutch solenoids I6 allowing core elements 96 to move inwardly into their casings l8 and permit the brake shoes 84 connected to core elements 94 to move out of indentations 83 in bearing sleeve 82 and thereby out of braking position. Simultaneously the engagement of the contacts of selector switch I530; will effect energization of the solenoid coil of uncouple switch Ifi' la to cause this switch to kick out and place the coupling system in neutral. The feathering switch I 56 is then actuated to place switch arm I41 in feather position and the propeller governor unit I4 will efiect feathering of the propeller It. The normal 'switch arm I48 will be open. The airplane can then be propelled entirely by the engine 3I'.

At such time as it is desired to re-c'oupl'e the propeller drive shaft I2 and the engine drive shaft 2 I as when coming in fora landing the pilot 15 will'first throttle the engine ill to idling speed and will move the feather switch arm I41 to disengaged position whereby the propeller It will be given a windmilling action. The couple switch I230. will next be operated to feed power to the synchronizing control unit 2'1. If the drive shaft I2 of the windmilling propeller II] and the engine drive shaft 2I are not rotating at the same speed the propeller alternator I8 and the engine alternator 24 will cooperate as in the coupling operation of the first embodiment of the invention described above to bring about synchronization of the speeds of the two shafts through the synchronizing control unit 2i. With any discrepancy between the speeds of shaft I2 and H a rotation of the magnetic field of hysteresis motor I65 will be effected which will cause the magnetic drag-cup III to rotate. Rotation of drag cup iii will operate through commutator I13 to feed impulses of current to the propeller control relay switch Il5, as hereinbefore described, and through the contact set I84, solenoids I16 and contact sets I'm-I19 pass corrective current to the propeller governor unit I4 to cause the latter to effect a change in the pitch setting of the propeller II] and thereby a change in its speed and the speed of its shaft I2. As synchronism between the speeds of propeller drive shaft I2 and engine drive shaft 2| is obtained current will cease to flow from the synchronizing control unit 2? to the propeller governor unit I4. With no current flowing in the propeller governor unit I4 the solenoid coil 2H of clutch controlling switch 204 will be deenergized permitting movable contact 208 to engage stationary contact 281 completing the circuit to solenoid coil 93 of clutch solenoid 'IB and thereby effect movement of the core element 54 outward from its casing I8. All the core elements 94 of the twelve solenoids I6 are actuated simultaneously; as has hereinbefore been stated, only one solenoid :8 has been shown for ease of description but the manner of operation of this one solenoid is characteristic of all. With the core elements 94 moving outwardly from their casings I8 the brake shoes 84 connected to the core elements 94 will be carried toward the braking surface 82 provided upon the exterior of engine drive shaft 2i. These brake shoes 84 will engage the brake sleeve 82 and move into a seat in the shallow indentations 83 provided by the bearing sleeve 82. With the seating of brake shoes 84 in indentations 83 contact 95 carried by core element 94 disengages from its associated contact IBI to break the circuit to solenoid coil I34 of motor actuating switch I21, deenergizing coil I34 and permitting movable contacts I28 and I29 to move under spring bias to engaged position whereby power can be supplied to the windings of motor 25 through couple switch I23a to operate said motor to rotate the worm drive 53. It is noted that the contacts 95 and IBI associated with the movable core elements 94 do not disengage until the brake shoes 84 are actually seated within an indentation 833. The springarm carried contact IOI maintains engagement with contact 95 until brake shoe 84 moves to its seat, at which time a stop I02 engages contact brake shoes t4 seated in indentations 83 the enam nes,

gine drive shaft 2I and the propeller drive shaft I2 will be driven at exactly the same speed and no variations in speed can occur. The splines of engine drive shaft 21 will be in exact alignment with the splines 44 of propeller drive shaft I2 so that when the coupling motor 25 operates to effect movement of the coupler element 41 into the propeller drive shaft I2 there will be a smooth and unobstructed movement out of the engine drive shaft 2I and onto splines 44 to effect the coupling of the two shafts I2 and 2I together. Thus there will be a first coupling of the engine drive shaft 2i and propeller drive shaft I2 through the clutch means 54 to insure proper alignment of splines 44 and 45 and then a final coupling through the coupler element 47 whereby power can then be effectively transmitted from the engine drive shaft 2I to propeller drive shaft I2.

After the coupling motor 25 has moved the coupler element 41 into coupling position limit switch I33 is operated to break the motor circuit, as has hereinbefore been described, to stop the operation of motor 25 and prepare it for reverse movement.

Also uponcompletion of the coupling action the thermal relay switch I58 will operate through flexing of its bimetallic member IGI to deenergize solenoid coil I of selector switch I53a to permit its contacts [54-455 to engage. Engagement of these contacts I54--I55 will energize the solenoid coil of couple switch I23a to cause it to throw said switch to circuit breaking position, to deen- I43 is actuated to normal position to again connect the pitch control switch I38 into circuit with the propeller governor unit I4 and thereby permit changes in propeller pitch to be made through the switch I38.

While certain preferred embodiments of the invention have been specifically disclosed, it is understood that the invention is not limited thereto as many variations will be readily apparent to those skilled in the art and the invention is to be given its broadest possible interpretation within the terms of the following claims.

Having thus described the invention what I claim as" new and desire to secure by Letters Patent is:

1. Means for coupling and uncoupling a rotatable propeller drive shaft havin a bore therein and a gas turbine drive shaft coaxially aligned therewith and also having a bore therein comprising means for effecting substantial synchronization between the speeds of rotation of said propeller drive shaft and the speed of rotation of said gas turbine engine drive shaft, and coupler means adapted to move within the bores of said drive shafts when they are rotating in substantial synchronism to effect coupling and uncoupling of said drive shafts.

2. Means for releasably coupling a hollow propeller shaft and a coaxially aligned hollow gas turbine engine drive shaft comprising means for effecting substantial synchronization between the speed of rotation of said propeller drive shaft and the speed of rotation of said gas turbine engine drive shaft, a reversibly movable coupler means movable within said drive shafts to effect coupling and uncoupling of said drive shafts, and motor means operatively connected to said coupler means for effecting reverse movement of said 17 coupler means between operative and inoperative positions.

3. Means for releasably coupling for common movement a propeller drive shaft having a bore therein and a coaxially aligned gas turbine engine drive shaft also having a bore therein comprising a plurality of annularly spaced longitudinal ribs disposed in said propeller drive shaft bore, a plurality of annularly spaced longitudinal ribs disposed in said engine drive shaft bore, means for effecting substantial synchronization between the speed of rotation of said propeller drive shaft and the speed ofirotation of said gas turbine engine drive shaft, a movable coupler means rectilinearly movable within the bores of said drive shafts and upon said ribs to effect coupling and uncoupling of said drive shafts, motor means, a rotatable means interconnecting said motor means and said rectilinearly movable coupler .means whereby said motor means can effect reverse movement of said coupler means between operative and inoperative'positions.

4. Means for releasably coupling for common movement a propeller drive shaft having abore therein and a coaXially alignedgas turbine engine drive .shaft also having a bore therein comprising a plurality of annularly spaced longitudinal ribs disposed in said propeller drive shaft bore, a plurality of annularly spaced longitudinal ribs disposed in said engine drive shaft bore, means for effecting substantial synchronization between the speed of rotation of said propellerdrive shaft and the speed of rotation of said gas turbine engine drive shaft, a movable coupler means disposed for movement within said bores and having peripheral longitudinal ribs provided thereon, said latter ribs cooperating with said ribs in the bores of said drive shafts to couple said drive shafts for common movement, and motor means having an operative connection with said coupler means and adapted to rectilinearly move said coupler means in reverse directions between operative and inoperative positions.

5. Means for releasably coupling for common movement a propeller drive shaft and a coaxially aligned gas turbine engine drive shaft comprising means for effecting substantial synchronization between the speed of rotation of said propeller drive shaft and the speed of rotation of said gas turbine engine drive shaft, a first coupling means controlled by said synchronizing means and operative after said propeller drive shaft and said gas turbine engine drive shaft are rotating in substantial synchronization for connecting said drive shafts together, and a second coupling means operative, after said first coupling means has effected connection of said drive shafts, to move to coupling position to connect said drive shafts.

6. Means for releasably coupling for common movement a propeller drive shaft having a bore therein and a coaxially aligned gas turbine engine drive shaft also having a bore therein comprising means for effecting substantial synchronization between the speed of rotation of said propeller drive shaft and the speed of rotation of said gas turbine engine drive shaft, a first coupling means carried upon the exterior of one of said drive shafts, operative after said propeller drive shaft and said gas turbine engine drive shaft are rotating in substantial synchronization, for connecting said drive shafts together, a second coupling means movable within said drive shafts and adapted to move to coupling position after said first coupling means has effected connection of said drive shafts, and motor mean for 18 moving said second coupling means in reverse directions between its operative and inoperative positions.

'7. Means for releasably coupling for common movement a propeller drive shaft and a coaxially aligned gas turbine engine drive shaft comprising means for effecting substantial synchronization'between the speed of rotation of said propeller drive shaft and the speed rotation of said gas turbine motor drive shaft, a first coupling means, controlled by said synchronizing means, for connecting said drive shafts together and adapted to operate when substantial synchronization between the speeds of rotation of said drive shafts has been'eifected, a second coupling means adapted to move to coupling position after said first coupling means has effected connection of said drive shafts, and motor means for moving said second coupling means in reverse direction between its operative and inoperative positions.

8. Means for coupling and uncoupling a propeller drive shaft having a bore therein and a gas turbine drive shaft coaxially aligned therewith and also having a bore therein comprising means for effecting substantial synchronization between the speeds of rotation of said propeller drive shaft and the speed of rotation of said gas turbine m0- tor drive shaft, a first coupling means carried upon the exterior of one of said drive shafts for effecting a connection between said drive shafts and adapted toimove to coupling position when substantial synchronization between the speeds of rotation of said drive shafts has been effected, a second coupling means movable within said drive shafts and adapted to move to coupling position after said first coupling means, and motor means for moving said second coupling means in reverse directions between operative and inoperative positions.

9. Means for releasably coupling a hollow rotatable propeller drive shaft and a coaxially aligned gas turbine engine hollow rotatable drive shaft comprising a plurality of longitudinal splines disposed in said propeller drive shaft and in said engine drive shaft, means for effecting substantial synchronization between the speed of rotation of said propeller drive shaft and the speed of rotation of said gas turbine engine drive shaft, means for effecting alignment of said splines provided in said drive shafts and coupler means engageable with said splines for connecting said drive shafts together for common movement and operable when said drive shafts are rotating in substantial synchronism to move to coupling position, and motor mean having an operative connection with said coupler means and adapted to move said coupler means in reverse directions between operative and inoperative positions.

10. Means for releasably coupling a propeller drive shaft and a coaxially aligned gas turbine engine drive shaft comprising mean for effecting substantial synchronization between the speed of rotation of said propeller drive shaft and the speed of rotation of said gas turbine engine drive shaft, coupler means operable to couple and uncouple said drive shafts when they are rotating in substantial synchronism, a motor operatively connected to said coupler means for moving it between operative and inoperative positions, control means for said motor for preventing operation thereof until said shafts are rotating in sub.- stantial synchronism, and means connecting said control means with said synchronization means.

pler means for effecting reverse movement of said I couplermeans between operative and inoperative positions, electric control means for said motor axially aligned gas turbine engine drive shaft comprising means for effecting substantial synchronization between the speed of rotation of said propeller drive shaft and the speed of rotation of said gas turbine engine drive shaft, coupler means operable to couple and uncouple said drive shaft when they are rotating in substantial synchronism, a motor operatively connected to said coupler means for moving it between operative and inoperative positions, a relay switch electrically connected to said motor for controlling the flow of current thereto having contact means adapted to be positioned in circuit-breaking position until said drive shafts are rotating in substantial synchronism, and means electrically connecting said relay switch with said synchronization means for controlling the movement of said relay switch contact between circuit-making and circuit-breaking positions.

OTTO WILLIAM EHLERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date Number Name 1,624,008 Ricker Apr. 12, 1927 1,680,209 Emmet Aug. 7, 1928 1,914,566 Haseltine June 20, 1933 2,017,997 Thomas Oct. 22, 1933 2,080,484 Hunt May 18, 1937 2,110,675 Pike Mar. 8, 1938 2,163,514 Farren June 20, 1939 2,253,578 Peterson et a1 Aug. 26, 1947 2,423,183 Forsyth July 1, 1947 2,426,008 Forsyth Aug. 19, 1947 2,427,846 Forsyth Sept. 23, 1947 2,465,538 Jensen Mar. 29, 1949 FOREIGN PATENTS Number Country Date 495,469 Great Britain Feb. 8, 1937 851,130 France Sept. 25, 1939 

